Vacuum tube



'June' 13, 1933. H. SIMON ET AL 1,914,218

VACUUM TUBE Filed April 6, 1927 Inventor-6:

Hellmut Simon,

Jakob Bingel,

Their Attorney Patented June 13, 1933 STATES PATENT OFFECE HELLMUT SIItTON, OF FRIEDENAU, AND JAKOB BINGEL, OECHARLOTTENBUBG, BERLIN,

GERMAIQY, ASSIGNORS TO GENERAL ELECTBIGOOMPANY, A CORPORATION OF NEW 7 YORK VACUUM. TUBE Application filed April 6, 1927, Serial No. 18].,510,'a nd in Germany '7, 1926.

The present invention relates to vacuum tubes, and more particularly to vacuum tubes adapted for use in the transmission of mes sages by radio. In the operation of vacuum tubes for radio transmission difficulty has sometimes been encountered with the circuits and tubes employed owing to the tendency of the grid or control elements of the tubes to emit secondary electrons. This secondary emission of the grid can not be avoided by the usual tube construction, and this is particularly true in the case of tubes having a thorium or oxide coated cathode. With such tubes a part of the active material of the cathode always vaporizes and deposits on the grid and the capacity of the grid to emit secondary electrons is thereby considerably 1ncreased. While attempts have been made to overcome this difficulty by changes in the circuit arrangements employed,these changes have been usually unsuccessful, since with different tubes of the same type the secondary electron currents have different values.

It is one of the objects of the present invention to provide means within the usual vacuum tube whereby an additional grid current may be produced which acts to prevent or neutralize the effect of secondary electron emission from the control or grid element of the tube.

The novel features which are characteristic of the present invention are set forth with particularity in the appendedclaim. The invention itself, however, will best be understood from reference to the following specification when considered in connection with the accompanying drawing in which Fig. 1 shows diagrammatically a usual form of circuit arrangement employed in wireless telephony; Fig. 2 shows the characteristic curves of the anode and grid currents in a vacuum tube; Fig. 3 shows the same characteristics when the grid or control element emits sec ondary electrons; Figs. 4, 5 and 6 show diagrammatical arrangements whereby the effect of the emission of secondary electrons from the grid may be substantially neutralized.

Referring to the drawing, we have indicated at R a usual form of vacuum tube com prising an evacuated receptacle having an anode A, grid G, and cathode K. In'the anode circuit a resistance R is indicated as a consuming device. A variable resistance R is inserted in the grid circuit. The tube R is separatelyexcited, that-is to say, high frequency current is impressed on the grid G and cathode K from a second tube not shown. With the arrangement disclosed in 1 failure of the tube, due to the emission of secondary electrons, sometimes occurs. This 1s due to the following causes: If F1g'.2'lS- cons1dered,1n wh1ch the usual characteristics of the anode current J, and of the grid current J are indicated it is seen that the grid current increases with increasing grid voltage; As soon as secondary electrons are emitted from the grid, the grid current characteristic changes its course in the manner indicated in Fig. 3. This necessitates that the voltage on the resistance R; in the grid circuit reverse. In other words, the grid or control element with rising grid current becomes more positive with reference to the cathode.

The anode current thereby increases considerably causing a bright incandescence of the anode, and, in fact, frequently fusing the anode so that the tube is destroyed. This action is commonly described as a break-down of the anode voltage. In order to overcome this defect without altering the circuit arrange ments usually employed, means are provided for producing an additional current in the tube which acts against any increase of secondary emission by the control element or grid. Referring more particularly to Fig. 4, we have shown the usual cathode 2 and grid 3 supported from a stem at one end of an electron discharge device, while the plate or anode member 4 is supported from a stem at the opposite end of the container. In this figure a rod 1 is positioned within the filament 2 and connected with the grid or control element 3. This rod provides additional or auxiliary grid current and has the property of attracting electrons when the grid is positive without giving off secondary electrons, since the anode action on the rod is weakened by the grid 3. Rod 1 moreover only receives electrons which are not involved in the utilization of the tube on account of the space charge between the different portions of the filament 2.

A secondary arrangement for neutralizing the effect of the emission of secondary electrons from the grid is disclosed in Fig. 5. In this arrangement a protective metal cylinder 5 is connected to the cathode so as to be at substantially cathode potential and is insert ed between the anode 4 and grid 8. A part of the grid is thereby withdrawn from the influence of the anode. The additional auxiliary grid current produced in this manner is approximately of such value that the grid current characteristic assumes the form shown in Fig. 2.

A similar action is obtained if the grid is partially provided with more or less large portions which are not permeable as, for example, a metal envelope 6. Electrons are attracted to this portion of the grid from the incandescent cathode. On the other hand, the secondary electrons arising from the inner side of the cylinder do not travel toward the anode, since the field of the anode only acts slightly around the edges of the cylinder 6.

What we claim as new and desire to secure by Letters Patent of the United States, is,-

An electron discharge tube comprising an anode, a cathode, a control electrode therebetween, and an electrode within said cathode and connected within the tube to said control electrode to neutralize the efiect of secondary emission from said control electrode.

In witness whereof, we have hereunto set our hands this 19th day of March, 1927.

HELLMUT SIMON. JAKOB BINGEL. 

